1. Field of the Invention
The present invention relates to a plurality of types of conveyor chain units (hereinafter simply referred to as the chain units) and a conveyor chain constructed of the plurality of types of the chain units, wherein the plurality of types of chain units are connected widthwise to form the conveyor chain which may vary in width of its conveying surface, depending upon the number and the types of the chain units used therein. More particularly, the present invention relates to two types of the chain units and a conveyor chain constructed of these two types of the chain units.
2. Description of the Prior Art
In U.S. Pat. No. 5,613,597 Palmer et al., there is disclosed a conveyor chain structured such that one or a plurality of chain units are connected in series in a widthwise direction. Each of the chain units has protruding open end portions alternately extending in a longitudinal direction from a central rib at a fixed pattern. Then, the chain units arranged in series are connected to each other by a rod extending in a widthwise direction with passing through the protruding open end portion so as to define a width of the conveyor chain. Further, the chain units are serially connected in a longitudinal direction with the chain rod extending to the protruding open end portion, so that a continuous conveyor chain belting is constructed.
The length which can be conveyed by the conveyor chain is limited by its own weight the strength of the conveyor chain itself and the frictional resistance due to the weight of the conveyed articles. The method of conveying an article can be divided into two ways comprising a side transfer in which a plurality of independent conveyor chains are installed partly adjacent to each other and a continuous transfer in which a plurality of independent conveyor chains are installed in nose-to-nose manner to each other.
FIG. 4 shows a state of the latter connecting method as seen from a lateral direction. In FIG. 4, conveyor chains A and B are independently driven by respective sprockets C and D, and in this embodiment, teeth TA and TB provided in the respective sprockets C and D commonly have a large number of teeth.
As is apparent from the drawing, it is impossible to completely remove a gap between the conveyor chains A and B. Further, the conveyor chain moves downward along the sprocket, whereby a recess generated between the conveyors A and B impedes a smooth transfer of the article between the conveyor chains.
One method for solving the problem is to provide a plate for preventing the recess between two conveyor chains in a portion having a height substantially the same height as that of the chain conveying surface. In U.S. Pat. No. 5,613,597 Palmer et al., there is further disclosed an improved chain unit in which the conveying surface of the chain unit is curved, whereby a surface of a portion of the conveyor chain engaging with the sprocket and folded back forms a substantially circular shape as seen from a lateral direction. Accordingly, a difference in level between the conveyor chains can be prevented by arranging the plate significantly close to the conveyor chain so as to make it possible to move and transfer the conveyed articles on the plate. However, in the case that a diameter of the sprocket is large, since it is necessary to make a length of the plate in the transfer direction relatively large, there is generated a problem that it is hard to smoothly transfer the article due to a friction between the plate surface and the article. Further, at a time of finishing the transfer operation, or discontinuing the transfer operation, the article is left on the plate and it is necessary to remove the article from the plate by a manual operation.
In order to solve such hung-up problem, for example, a radius R of the sprocket is made small and the plate is used as rarely as possible or an interlinking width thereof is made small if the plate is used. However, in order to reduce the radium, it is necessary to narrow the interval between the adjacent teeth or make a size of the tooth itself small. In the case of narrowing the interval between the teeth, it is necessary to make a longitudinal pitch of the conveyor chain in correspondence to the interval, and it is necessary to secure a sufficient space at which the teeth of the sprocket can be inserted and engaged, in each of the chain units within the reduced pitch. However, in this case, since an amount of a plastic mold of the chain unit itself is reduced and a total strength is reduced, it is hard to sufficiently secure a strength for a wide or long continuous conveyor chain to convey articles, so that a service life of the conveyor chain is greatly affected.
On the contrary, in place of applying the space at which the tooth can be inserted into the chain unit, it is one method to make the tooth of the sprocket small, however, in this case, the strength of the sprocket itself is reduced and the service life thereof is deteriorated.
Then, in order to maintain the interval between the adjacent teeth of the sprocket as far as possible while reducing the diameter of the sprocket, it has been considered as one means that a number of the teeth of the sprocket is reduced at the same time. However, in this case, the following problem is generated.
FIG. 5 is a graph which shows a speed fluctuation rate at which the conveyor chain performs in correspondence to a difference of the number of the teeth of the sprocket having the same radius. When the number of the teeth is increased, it is possible to perform at a relatively continuous speed having a little change, however, the speed fluctuation rate exponentially becomes high. In this embodiment, in the case of the number of the teeth is 24, the speed fluctuation rate is 0.8%, however, the speed fluctuation rate when the minimum number of the teeth is 6 is 13%. Accordingly, when using the sprocket having a small number of teeth, a discontinuous knocking speed with a large fluctuation occurs, so that it is hard to smoothly convey a commodity. As a result, the commodity itself is broken or a load is increased due to a vibration applied to the conveyor chain, so that the service life of the conveyor chain is deteriorated.
Accordingly, an object of the present invention is to provide a chain unit in which an interconnection plate is not required or a width of the interconnection plate is significantly reduced if it is used, a transfer of an article to be transferred between opposed conveyor chains is made easy, and a fluctuation rate of a performance speed can be made small.
Further, another object of the present invention is to provide an improved chain unit in which a high accuracy can be secured while providing a sufficient space at which teeth of a sprocket can be engaged, even at a reduced pitch.
In addition, the other object of the present invention is to provide an improved chain unit which can be easily assembled with a high interconnection strength and without depending upon a direction of a mutual combination in comparison with a conventional chain unit which can construct a conveyor chain having a desired width by connecting in a zigzag manner.